Method for maintaining catalytic activity during a hydrosilylation reaction

Abstract: A method for maintaining catalytic activity during a hydrosilylation reaction between a silicon hydride and an unsaturated compound is disclosed. The method comprises reacting a silicon hydride and an unsaturated compound in the presence of a platinum catalyst wherein a peroxide is added into the reaction mixture to maintain the catalytic activity of the platinum catalyst.

Description: One method in the art for producing organosilicon compounds comprises reacting a silicon hydride compound with an unsaturated compound in the presence of a catalyst. This reaction is commonly referred to as hydrosilylation. Typically, the catalyst is platinum metal on a support, a platinum compound generally used in an inert solvent, or a platinum complex. However, other catalysts comprising rhodium or nickel may be used. The prior art of these catalysts is represented by US-A 2,823,218; US-A 3,220,972 and EP-A 0 337 197. One of the major problems with hydrosilylation is the deactivation of the catalyst prior to completion of the reaction. One accepted method for catalyst reactivation has been to expose the reaction mixture to oxygen. For example, US-A 4,578,497 teaches the use of an oxygenated, platinum-containing catalyst for hydrosilylation reactions. The use of peroxides to activate reactions that are otherwise unreactive using metallic catalysts is known for several reactants and catalysts. In these situations there is no catalytic activity in the absence of the peroxide. Thus, the peroxide is introduced to "start" or activate the reaction rather than to maintain catalytic activity. This prior art is represented by the following journal articles: Licchelli et al., "Catalyzed Hydrosilylation of 2-Methyl-1-buten-3-yne with Methyldichlorosilane; Promotional Effect Imparted by the Presence of a Different Chlorosilane", Tetrahedron Letters, Vol.28, No. 2, pp.3719-3722 (1987); Dickers et al., "Organosilicon Chemistry, Part 24, Homogeneous Rhodium-catalyzed Hydrosilation of Alkenes and Alkynes: Role of Oxygen or Hydroperoxides", J.C.S. Dalton, pp. 308-313 (1980); and Calhoun et al., "Organic Peroxide Assisted Transition Metal Hydrosilylation Catalysis", Transition Met. Chem., 8, 365-368(1983). An object of this invention is to provide a method for maintaining catalytic activity during a hydrosilylation reaction wherein the hydrosilylation reaction comprises reacting a silicon hydride having 1 to 3 hydrogen atoms attached to the silicon with unsaturated compounds in the presence of a platinum catalyst and a peroxide. Our invention introduces a method of maintaining catalytic activity in a hydrosilylation reaction wherein the reaction comprises reacting silicon hydrides having 1 to 3 hydrogen atoms attached to the silicon with unsaturated compounds to produce organosilicon compounds. The reaction is catalyzed using a platinum catalyst selected from platinum metal, platinum compounds and platinum complexes. A peroxide is added to maintain the catalytic activity until one or both of the reactants are consumed. This invention is directed to a method of maintaining catalytic activity in a hydrosilylation reaction mixture by introducing a peroxide into the reaction mixture said hydrosilylation reaction comprising, reacting: (A) a silicon hydride selected from silicon hydrides having the general formulae: wherein each R is independently selected from substituted and unsubstituted alkyl groups having 1 to 30 carbon atoms, substituted and unsubstituted cycloalkyl groups having at least 4 carbon atoms and substituted and unsubstituted aryl groups having 6 to 16 carbon atoms; each R' is independently selected from alkyl groups having 1 to 6 carbon atoms; R'' is independently selected from R and the hydrogen atom, with the proviso that at least one R'' in each molecule is a hydrogen atom; X is a halide; p has a value of at least one; q has a value of at least 1 with the proviso that p+q has a value of 3 to 8; r has a value of 3 to 8; s has a value of 1 or greater; t has a value of 1 or greater; u has a value of 1, 2, or 3 with the proviso that u+y≤3 ; v has a value of zero or an integer of 1 or greater; w has a value of 1 to 3; x has the value of 1 to 3; y has a value of 0 to 2; and z has a value of 0 to 2 with the proviso that w+z≤3 , with (B) unsaturated compounds selected from (i) substituted or unsubstituted unsaturated organic compounds or mixtures thereof, (ii) substituted or unsubstituted unsaturated silicon compounds or mixtures thereof and, (iii) mixtures of (i) and (ii); in the presence of (C) a hydrosilylation catalyst selected from (a) platinum metal on a support, (b) platinum compounds, and (c) platinum complexes; wherein a peroxide is added to the reaction mixture whereby said hydrosilylation reaction is maintained. Silicon hydrides useful in the instant invention may be exemplified by compounds or mixtures of compounds of the formulae: The silicon hydrides useful in the instant invention are trimethylsilane, dimethylphenylsilane, dimethylsilane, dichlorosilane, dimethoxysilane, methyldimethoxysilane, triethylsilane, triethoxysilane, trichlorosilane, methyldichlorosilane, dimethylchlorosilane, trimethoxysilane, 1,1,1,2,3,3,3- heptamethyltrisiloxane, dimethylsiloxane/methylhydrogensiloxane copolymers and methylhydrogencyclic siloxanes. This silicon hydride is then reacted with unsaturated compounds selected from (i) substituted or unsubstituted unsaturated organic compounds or mixtures thereof, (ii) substituted or unsubstituted unsaturated silicon compounds or mixtures thereof and, (iii) mixtures of (i) and (ii). More specific examples of unsaturated compounds are unsubstituted cycloalkenyl compounds having at least 4 carbon atoms, substituted cycloalkenyl compounds having at least 4 carbon atoms, linear alkenyl compounds having 2 to 30 carbon atoms, branched alkenyl compounds having 4 to 30 carbon atoms, and mixtures thereof. The substituted and unsubstituted cycloalkenyl compounds useful in our invention are those olefins that contain one or more unsaturated carbon-carbon bond in the ring. The unsubstituted cycloalkenyl compounds are further exemplified by cyclobutene, cyclopentene, cyclohexene, cycloheptene, cyclooctene, cyclopentadiene, 1,3-cyclohexadiene, 1,3,5,7-cycloheptadiene and cyclooctatetraene. The substituted cycloalkenyl compounds useful in the instant invention are only those that contain substitution on the saturated carbons (i.e., not at the C=C bond). The substituted unsaturated alicyclic compounds useful in the instant invention is further exemplified by 3-methylcyclopentene, 3-chlorocyclobutene, 4-phenyl-cyclohexene and 3-methylcyclopentadiene. The preferred cycloalkenyl compounds are cyclohexene and cyclopentene. These unsaturated cycloalkenyl compounds are commercially available. Prior to reaction, the unsaturated cycloalkenyl compound may be treated or purified. Methods for treating or purifying the unsaturated cycloalkenyl compound are known in the art and include distillation, treatment with alumina and others. Other compounds that are useful in our invention are unsaturated linear and branched alkyl compounds which include those compounds with terminal unsaturation such as 1-hexene, those compounds with internal unsaturation such as trans-2-hexene and unsaturated aryl containing compounds such as styrene and α-methylstyrene. Other unsaturated compounds useful in the invention include olefinically unsaturated functional alkenyl compounds which contain halogen, oxygen in the form of acids, anhydrides, alcohols, esters, ethers and nitrogen. The halogenated olefinically unsaturated functional alkenyl compounds used herein are exemplified by compounds such as vinyl chloride, allyl chloride, allyl bromide, allyl iodide, allylene bromide, methallyl chloride, tri- and tetra- chloroethylene, tetrafluoroethylene, chloroprene, vinylidene chloride, and dichlorostyrene. Suitable oxygen containing olefinically unsaturated functional alkenyl compounds are ethers such as the allyl and vinyl ethers; alcohols such as allyl alcohol (vinyl carbinol), methylvinylcarbinol and ethynyldimethylcarbinol; acids such as acrylic, methacrylic, vinylacetic, oleic, sorbic and linolenic; and esters such as vinyl acetate, allyl acetate, butenyl acetate, allyl stearate, methylacrylate, ethylcrotonate, diallyl succinate and diallyl phthalate. Suitable nitrogen containing olefinically unsaturated functional alkenyl compounds include indigo, indole, acrylonitrile and allyl cyanide. Specifically included within the definition of olefinic unsaturated groups are those olefinic unsaturated groups that are substituted by organofunctional moieties such as and the like. Unsaturated silicon compounds useful in this invention are (CH 2 =CH) a Si(OR') 3-a wherein R' has the same meaning as that set forth above and a has a value of 1 or 2, CH 2 =CHCH 2 Si(OR') 3 and CH 2 =CHCH 2 Si(CH 3 )(OR') 2 . These unsaturated compounds are commercially available. Prior to the reaction of the unsaturated compound it may be preferable to treat or purify the unsaturated compound. Methods for treating or purifying the unsaturated compound are those methods known in the art and include distillation, treatment with alumina and others. The relative amounts of silicon hydride and unsaturated compound employed in our process have no technical limitations. One unsaturated linkage, for example ethylene, is obviously the stoichiometric requirement per silicon bonded hydrogen atom. However there is no absolute necessity for equivalent amounts of the reactants to be employed and any desired excess of either reactant can be present. In fact, an excess of one reactant, typically the unsaturated compound, may often be desirable to force the reaction to completion or to make the greatest use of the reactant which is the most expensive or most rare. Thus, the choice of reactant ratios is a matter of practicality and economics based upon the reactants employed. It is preferred to use a reactant ratio ranging from 1:20 to 20:1 in terms of equivalents of Si-H compound to unsaturated compound, the operating range being preferably in the region of from 1:2 to 2:1. In some cases it is desirable to also employ a solvent for one or both of the reactants. The amount of solvent employed is not critical and can vary without limit except for economic considerations. Any solvent can be employed which will dissolve, but remain inert toward the desired reactants under the conditions of the reaction and which will not interfere with the reaction. The solvent should also be selected so that easy separation of the products after the reaction can occur. The reaction between the silicon hydride and unsaturated compound is catalyzed using a hydrosilylation catalyst. Hydrosilylation catalysts useful in our invention are exemplified by platinum metal, platinum compounds and platinum complexes. The platinum compounds and platinum complexes are exemplified by chloroplatinic acid, chloroplatinic acid hexahydrate, Karstedt's catalyst (Pt #2, Pt(ViMe 2 SiOSiViMe 2 ) 2 ), dichlorobis(triphenylphosphine) - platinum (II), cis-dichloro-bis(acetonitrile)platinum(II), dicarbonyldichloroplatinum(II), platinum chloride and platinum oxide. The platinum metal can be deposited on a support such as charcoal, alumina, zirconia, carbon, silica gel, nylon and polyacrylonitrile. Any platinum containing material which effects the reaction between the silicon hydride and the unsaturated portion of the unsaturated compound is useful in this invention. Suitable amounts of platinum containing compounds and platinum complexes vary within wide limits. Concentrations on the order of 1 mole of catalyst (providing one mole of platinum) per billion moles of unsaturated groups in the unsaturated compound are useful. Concentrations as high as 1 to 10 moles of catalyst per thousand moles of unsaturated groups in the unsaturated compound are also employed. Generally, the economics of the reaction dictates the particular level of catalyst employed. Preferable concentrations are from 1 mole of platinum per 1,000 moles of unsaturated groups to 1 mole of platinum per 1,000,000 moles of unsaturated groups in the unsaturated compound. Suitable amounts of supported platinum include from at least 0.1 weight percent, preferably 0.1 to 10 weight percent, more preferably from about 0.5 to 5 weight percent, based upon elemental platinum. A further description of platinum catalysts useful in the instant invention is found in US-A(s) 4,578,497, 3,775,452, 3,220,972 and 2,823,218. The catalyst may be dissolved in a solvent for ease of handling and to facilitate measuring the minute amounts needed. Preferably the solvent should be inert. Suitable solvents include hydrocarbon solvents such as benzene, toluene, xylene, mineral spirits and polar solvents such as alcohols, various glycols and esters. In the instant invention, the reaction is carried out in the continuous presence of a peroxide. The peroxide, when added during the course of the reaction, provides a means for maintaining the catalytic activity during the reaction. Peroxides useful in our invention are exemplified by organic peroxides and hydroperoxides such as t-butyl hydroperoxide, t-amyl hydroperoxide and di-t-butyl peroxide; diacyl peroxides such as dibenzoyl peroxide and diacetyl peroxide; and other peroxides or hydroperoxides. The amount of peroxide added will be dependent on the operating conditions, the reactants and the amount of catalyst present. Typically, 0.05 to 10 weight parts peroxide per 100 weight parts of reactants are used, preferably 0.1 to 1 weight parts peroxide per 100 weight parts of reactants. The peroxides are typically admixed with the reactants prior to introduction into the reaction vessel; however, the peroxide may be added separately to the reaction vessel from the reactants. The reaction temperature can vary over an extremely wide range. The temperature will affect the life of the peroxide and is therefore dependant on the type of peroxide being employed. The optimum temperature also depends upon the concentration of catalyst present, concentration of peroxide and the nature of the reactants. Best results are obtained by initiating the reaction at 20° to 250°C and maintaining the reaction within the limits of this range. The reaction is typically exothermic and the reaction temperature can be maintained by controlling the rate of addition of one of the reactants or applying cooling means to the reaction vessel. It is preferred although not necessary, when operating at atmospheric pressure, to use an operating temperature such that the reaction is carried out under reflux conditions. The reaction can be carried out at atmospheric, subatmospheric, or superatmospheric pressures. The choice of conditions is largely a matter of choice based on the nature of the reactants and the equipment available. Non-volatile reactants are especially adaptable to being heated at atmospheric pressure. It may be preferred under certain conditions to run the reaction at pressures above atmospheric to reduce the volatility of the reactants at higher temperatures. The amount of time for the reaction to go to completion depends upon the reactants, reaction temperature, catalyst concentration, and peroxide concentration. Determination of when the reaction has gone to completion can be accomplished by simple analytical methods such as gas liquid chromatography or by infrared spectrometry. The reaction may be run on a continuous, semi-continuous or batch reactor. A continuous reactor comprises a means wherein the reactants are introduced and products are withdrawn simultaneously. The continuous reactor may be a tank, a tubular structure, a tower, or another structure, the overall design not being essential. A semi-continuous reactor comprises a means wherein some of the reactants or a reaction heel are charged at the beginning and the remaining reactants are fed continuously as the reaction progresses. The product may be simultaneously withdrawn from the semi-continuous reactor. A batch reactor comprises a means wherein all the reactants are added at the beginning and processing is carried out according to a predetermined course of reaction during which reaction no reactant is fed into or removed from the reactor. Typically, a batch reactor will be a tank with or without agitation means. EXAMPLE 1 A mixture of 37,959 grams (330 moles) of MeHSiCl 2 and 20,199 grams (264 moles) of allyl chloride was pressurized to 69 kPa (10 psi) with nitrogen and was pumped at a rate of approximately 1570 grams/hour at a pressure of 2.1 to 2.4 MPa (300 to 350 psi) into 160 grams of 1% Pt/2.4-4.8 mm (4-8 mesh) carbon contained in a 2.5 cm x 68.6 cm (1" x 27") stainless steel pipe heated to 100°C. in boiling water. At the start of the run the hottest part of the catalyst bed ranged from 190 to 210°C. About half way through the run, the temperature decreased to 170°C. and by the end of the run the temperature had decreased to 154 to 163°C. The temperature change of the catalyst bed was very gradual. Benzoyl peroxide (BzO 2 ), 1 gram per 1,000 gram mixed reactants, was added during the first 18.34 hours of the run. The concentration of benzoyl peroxide was increased to 2 gram per 1,000 gram of mixed reactants for the next 4.85 hours. Di-t-butyl peroxide (DBP), 2 grams per 1,000 grams mixed reactants was then added for the next 2.17 hours. The use of peroxide was then discontinued for the remaining 11.64 hours of the run. Table 1 shows the composition of the reaction product at the various times during the run. A total of 41.25 grams (0.16 mole) of benzoyl peroxide and 5.28 g (0.36 mole) di-t-butyl peroxide were employed. At the end of the experiment 2.4 x 10 -5 moles of platinum per mole of silane had been utilized. V.P.C. Area% Composition Time (hrs) Peroxide Used Propylene MeSiHCl 2 and Allyl Chloride MeSiCl 3 PrMeSiCl 2 Cl(CH 2 ) 3 SiMeCl 2 18.3 BzO 2 (0.1%) 0.93 2.91 18.36 19.43 58.7 4.9 BzO 2 (0.2%) 1.1 6.7 17.6 17.2 57.5 2.2 DBP (0.2%) 1.7 7.25 17.9 16.15 56.95 11.6 none 1.5 15.0 17.3 14.6 51.5 COMPARATIVE EXAMPLE 1 A mixture of 14,050 grams (122 moles) of MeHSiCl 2 and 6,555 grams (85.6 moles) of allyl chloride was pressurized to 69 kPa (10 psi) with nitrogen and pumped at 2.1 MPa (300 psi) into 1% Pt/2.4-4.8 mm (4-8 mesh) carbon contained in a 2.5 cm x 68.6 cm (1" x 27") stainless steel pipe heated to 80°C. in boiling water. The system ran well for the first 10 hours at a reactant flow rate of 600 to 1100 g/hour producing a crude product which contained 53 area% chloropropylmethyldichlorosilane. During the next 2 hours, at flow rates of 600 to 800 g/hr, the catalyst deactivated resulting in a crude product containing less than 20 area% chloropropylmethyldichlorosilane. Analysis of the catalyst by emission spectroscopy showed 0.5% Pt in the deactivated catalyst. The deactivated catalyst was removed and replaced with 146 grams of fresh 1% Pt/C. The remainder of the column was filled with porcelain saddles to prevent agitation of the catalyst granules. The fresh catalyst was wetted with 140 ml. of crude ClCH 2 CH 2 CH 2 SiMeCl 2 . A mixture of 10,825 grams (94.2 moles) of MeHSiCl 2 and 5,400 grams (70.6 moles) of allyl chloride was added to the unused reactants. The combined mixture was pressurized to 69 kPa (10 psi) with nitrogen and pumped at 2.1 MPa (300 psi) into the 146 grams of 1% Pt/2.4-4.8 mm (4-8 mesh) carbon catalyst contained in the 2.5 cm x 68.6 cm (1" x 27") stainless steel pipe heated to 90°C. in boiling water. The reaction was exothermic and further heating was not necessary to maintain the water bath at 90 to 95°C. The system was run for a total of 23 hours over a period of 5 days. During the first 10 hours, the system was operated at feed rates up to 1600 g/hr. of mixed reactants obtaining a crude which contained 52 to 60 area% chloropropylmethyldichlorosilane. After 13 hours of operation, the feed rate had to be slowly reduced to 440 g/hr. to maintain greater than 50 area% chloropropylmethyldichlorosilane showing that loss of catalyst activity was occurring. A product quantity of 22,154 grams was obtained while only 60 ml of material was collected in the cold trap. Analysis of the catalyst by emission spectroscopy showed 0.47% Pt.

Claims: A method of maintaining catalytic activity during a hydrosilylation reaction by adding a peroxide into the hydrosilylation reaction wherein the hydrosilylation reaction comprises, reacting: (A) a silicon hydride selected from silicon hydrides having the general formulae: wherein each R is independently selected from substituted and unsubstituted alkyl groups having 1 to 30 carbon atoms, substituted and unsubstituted cycloalkyl groups having at least 4 carbon atoms and substituted and unsubstituted aryl groups having 6 to 16 carbon atoms; each R' is independently selected from alkyl groups having 1 to 6 carbon atoms; R'' is independently selected from R and the hydrogen atom, with the proviso that at least one R'' in each molecule is a hydrogen atom; X is a halide; p has a value of at least one; q has a value of at least 1 with the proviso that p+q has a value of 3 to 8; r has a value of 3 to 8; s has a value of 1 or greater; t has a value of 1 or greater; u has a value of 1, 2, or 3 with the proviso that u+y≤3 ; v has a value of zero or an integer of 1 or greater; w has a value of 1 to 3; x has the value of 1 to 3; y has a value of 0 to 2; and z has a value of 0 to 2 with the proviso that w+z≤3 , with (B) unsaturated compounds selected from (i) substituted or unsubstituted unsaturated organic compounds or mixtures thereof, (ii) substituted or unsubstituted unsaturated silicon compounds or mixtures thereof and, (iii) mixtures of (i) and (ii); in the presence of (C) a hydrosilylation catalyst selected from (a) platinum metal on a support, (b) platinum compounds, and (c) platinum complexes; wherein a peroxide is added to the reaction mixture whereby said hydrosilylation reaction is maintained. A method as claimed in claim 1 wherein the silicon hydride has the formula R y H u SiX 4-y-u wherein each R is independently selected from substituted and unsubstituted alkyl groups having 1 to 30 carbon atoms, substituted and unsubstituted cycloalkyl groups having at least 4 carbon atoms and substituted and unsubstituted aryl groups having 6 to 16 carbon atoms; X is a halide; u has a value of 1, 2, or 3 with the proviso that u+y≤3 ; and y has a value of 0 to 2. A method as claimed in claim 2 wherein the silicon hydride is methyldichlorosilane and the hydrosilylation catalyst is platinum metal on a charcoal support. A method as claimed in claim 1 wherein the unsaturated compound is a halogenated olefinically unsaturated alkenyl compound and the peroxide is benzoyl peroxide. A method as claimed in claim 4 wherein the unsaturated compound is allyl chloride. A method as claimed in claim 1 wherein ingredient (A) is silicon hydride having the general formulae: R y H u SiX 4-y-u wherein each R is independently selected from substituted and unsubstituted alkyl groups having 1 to 30 carbon atoms, substituted and unsubstituted cycloalkyl groups having at least 4 carbon atoms and substituted and unsubstituted aryl groups having 6 to 16 carbon atoms; X is a halide; u has a value of 1, 2, or 3 with the proviso that u+y≤3 ; and y has a value of 0 to 2; ingredient (B) is a halogenated olefinically unsaturated alkenyl compound; ingredient (C) is a hydrosilylation catalyst selected from platinum metal on a support. A method as claimed in claim 1 wherein ingredient (A) is methyldichlorosilane; ingredient (B) is allyl chloride; ingredient (C) is a hydrosilylation catalyst of platinum metal on charcoal and the peroxide is di-t-butyl peroxide.

Inventors: BANK HOWARD MARVIN, BANK, HOWARD MARVIN
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1994
Main classification: C07F7
IPC codes: C07F7, B01J27, B01J23, C08K5, B01J31, C08L83